The invention relates to a high-voltage power breaker having a first and a second rated current contact piece, which are coaxially opposite one another, and having a first and a second arc contact piece, which are likewise coaxially opposite one another, in which case at least the first rated current contact piece and the first arc contact piece which is associated with it can be driven, and in which case the first arc contact piece is connected to an insulating nozzle for blowing out an arc which is struck between the two arc contact pieces, which insulating nozzle projects, at least partially in the disconnected state, into the isolating gap between the first rated current contact piece and the first arc contact piece on the one hand, and between the second rated current contact piece and the second arc contact piece on the other hand.
Such a high-voltage power breaker is known, for example, from U.S. Pat. No. 5,478,980 and U.S. Pat. No. 5,654,532.
In the known embodiments of high-voltage power breakers, a contact pin projects into the nozzle, and blocks it, in the connected state. During the disconnection process, the nozzle is moved together with the first arc contact and the first rated current contact, so that the constriction of the nozzle by the arc contact, which is in the form of a pin, is released.
In the disconnected state, the insulating nozzle bridges the isolating gap and in each case has a field electrode in the form of an annular body at its free end, which metal body makes electrically conductive contact, by means of a sliding contact, on the contact side of the second arc contact piece and of the second rated current contact piece.
In this way, the respective annular shielding body forms a field electrode in the disconnected state, which field electrode limits the isolating gap on the side of the second rated current contact, and shields the contact arrangement.
The aim of this is to control the electric field in the area of the isolating gap in such a manner that no excessive field loads can occur on the contact pieces.
The present invention is based on the object of providing field control in the area of the isolating gap using physically simple means and at a low price.
According to the invention, the object is achieved by the insulating nozzle having an annular filling body, which is attached detachably on its outer circumference and is composed of an insulating material having a dielectric constant xcex5r greater than 1, in particular xcex5r greater than 3.
A filling body such as this, which is composed of an insulating material having a dielectric constant which is greater than that of the insulating gas, makes the electric field between the contact pieces uniform in such a manner that the contact pieces themselves, in particular the arc contact pieces and especially the second arc contact piece, are dielectrically relieved of the load.
This is not done by providing equipotential surfaces, as would be the situation as a result of the geometry of a field electrode according to the prior art, but by the capability to influence the lines of force by the difference between the dialectric constant of the insulating gas on the one hand and that of the filling body on the other hand.
One advantage over the use of a field electrode is that the filling body does not need to be brought into electrical contact. Electrical contact, as is normal in the case of field electrodes, would be pointless since the filling body is not conductive.
A further advantage of a filling body which is detachably attached to the circumference of the insulating nozzle is that the insulating nozzle can itself be produced in slimline form, such that it is simple to fit in the interrupter unit. This is particularly important if the insulating nozzle is to be pushed in through a narrow opening during assembling, to the edge of which opening it is attached by means of a step on the insulating nozzle. Since the diameter of the filling body is larger than that of the insulating nozzle, it would be virtually impossible to fit the insulating nozzle with a filling body arranged in a fixed manner on it.
The configuration according to the invention allows the insulating nozzle to be fit first of all, with the filling body being fit on it later, during the assembly process.
A further advantage of a filling body composed of insulating material over a field electrode is that the filling body can be produced from a lightweight material, thus keeping down the mass to be accelerated during operation of the power breaker.
Further advantageous refinements of the invention are described in the dependent claims.